The present invention relates to an interface device of the type commercially designated as the "Centronics" type. It is used, for example, in a printer or a plotter for sending and receiving data to and from external electronic equipment employing a microcomputer connected to the printer or plotter, based upon a communication system having what is commercially designated as the "Centronics Specification".
In general, the system of communicating parallel data by handshaking, which is based on the so-called Centronics specification, is well known as one specification used in communication systems between a printer or plotter and external electronic equipment employing a microcomputer. In the communication system based on the Centronics Specification, the timing relationships for each of the enabling signals ACK and BUSY, which are standards of handshaking, include three patterns as generally shown in FIGS. 3A, 3B and 3C. Normally, the Centronics type interface in one printer or plotter outputs said signals by any one of the timing patterns as shown in FIGS. 3A, 3B and 3C.
However, in case the printer or plotter performing communication by the timing relationship shown in FIG. 3B is connected to the external electronic equipment performing communication by the timing relationship shown in FIG. 3A, no handshaking can be performed because of the different timing relationships of the ACK and BUSY signals. Accordingly, the printer or plotter having the Centronics type interface cannot always communicate with the external electronic equipment using a communicating means based on the Centronics specification.
The present invention has been made in the light of the above-mentioned problems, and makes the timing relationships of the signals operate in accordance with the standards of handshaking so that the signals can be received by the external electronic equipment, provided the communicating means based on the Centronics Specification agrees with the timing relationships of the signals for handshaking outputted from the printer or plotter in case these timing relationships of the signals differ.